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Drained Timber Pile Ground Improvement for Liquefaction Mitigation

This project will improve ground stability by using drained timber piles to improve densification in surrounding contractive soils by draining construction-induced excess pore pressures as well as excess pore pressures generated during earthquake-induced ground motions. The work will be carried out in two stages. Work in Stage 1 will focus on developing drained timber pile prototypes and evaluating their effectiveness in improving soil densification at a selected test site for factors such as spacing, drainage, and time. The work will begin with the development of several drained timber pile prototypes, which will be evaluated for their robustness against installation damage. A suitable test site for full-scale evaluation of selected timber pile prototypes will be identified with assistance from collaborating industrial partners. The site subsurface will be assessed through a series of tests, including soil borings with sampling, cone penetration, and shear velocity soundings. The next task will investigate the effect of spacing, drainage, and time-dependence on the degree of densification achieved with drained displacement piling. Conventional displacement pilings will also be evaluated for comparison. Work in Stage 2 will further investigate the effect of spacing and drainage on the reduction of blast-induced pore pressures followed by application of analytical methods to predict densification pore pressure reduction and comparing analytical data with actual field results. At lease 25 borings will be drilled and packed with small explosive charges to raise the pore pressure. The generation of excess pore pressures is expected to decrease with decrease in pile spacing and, for a given pore pressure, blast-induced excess pore pressures will be smaller in the zones improved with drained piles as compared to conventional piles. Finally, analytical techniques, including finite element modeling, will be used to predict the amount of densification and pore pressure reduction. The predicted values will be compared with those obtained in field experiments. By showing that pore pressures can be adequately predicted using these modeling techniques, contractors and departments of transportation (DOTs) will have strong guidance with which to aid planning and design of drained timber displacement pile ground improvement.